摘要:

The profiles of AlGaAs/GaAs heterostructures grown by gas‐source molecular beam epitaxy (GSMBE) on patterned substrates at different growth temperatures have been studied. It was found that at higher substrate temperature, the GSMBE growth results in Al clustering and the formation of high index planes. With a proper combination of low growth temperature and etched profile, a quasiplanarized surface is obtainable. A process simulation program is found to be capable of simulating the GSMBE growth profile at lower substrate temperature with reasonable accuracy.

ISSN:0021-8979    

DOI:10.1063/1.354739

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Si delta‐doped layers of GaAs were grown by low pressure metal organic vapor phase epitaxy (LP‐MOVPE). The results showed that, in LP‐MOVPE, growth rate plays a crucial role in confinement of dopants and growth temperature has only a secondary effect. Effects of purge time, doping temperature, and doping period on sheet carrier concentration of delta‐doped layers were studied. The effect of growth rate on confinement of dopants was discussed.

ISSN:0021-8979    

DOI:10.1063/1.354740

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Channeling of H+and H2+ions of energies between 1.0 and 2.0 MeV in ⟨100⟩‐textured polycrystalline diamond films grown by microwave plasma‐assisted chemical‐vapor deposition has been observed with Rutherford backscattering. The width of the orientational distribution of the diamond crystallites as deduced from the measured projectile velocity dependence of the observed channeling angular scans amounted to about 1°.

ISSN:0021-8979    

DOI:10.1063/1.354741

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report for the first time a double 45°‐cut mutually pumped phase conjugate mirror, which has high phase conjugate reflectivities and is highly insensitive to the alignment of the two incident beams. For example, two mutually incoherent incident beams can produce their own phase conjugate outputs when the angle between the incident beams is varied from as much as 7° to 140° and over 60% conjugate reflectivity can be obtained. Furthermore, the phase conjugate outputs are stable because the competition from the self‐pumped phase conjugation can be avoided easily.

ISSN:0021-8979    

DOI:10.1063/1.354742

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Efficient optical limitation is demonstrated in the toluene solution of C60based on the reverse saturable absorption. The highly nonlinear absorption can be used to smooth a spike‐like pulse in the nanosecond region. Optical bistability is obtained in a nonlinear Fabry–Perot cavity filled with a thin layer of polystyrene doped with C60/C70. A smooth pulse with 25 ns width (full width at half‐maximum) is compressed to 15 ns and a spike‐like pulse is subjected a wave form distortion by this device. The light limitation effect in this polystyrene layer 0.3 mm thick was demonstrated at the wavelength of 532 nm and the threshold about 20 mJ/cm2.

ISSN:0021-8979    

DOI:10.1063/1.354743

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The BaTiO3ferroelectric films of quality suitable for applying as dielectrics in 64 and 256 Mb dynamic random access memory have been successfully synthesized using the laser ablation technique. The dielectric constant and dielectric strength of the films are &egr;=200 and 1 MV/cm, respectively. The switching characteristics areQc=0.66 &mgr;c/cm2,ts=0.1 ps, andJ1=1.57 &mgr;A/cm2at 2.5 V, for charge storage density, writing time, and leakage current density, respectively. The quality of the BaTiO3films is superior to the Ta2O5dielectric films and is comparable to the lead‐zirconate‐titanate ferroelectric films.

ISSN:0021-8979    

DOI:10.1063/1.354744

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Solitons are nonlinear propagating wave pulses that preserve their shape without spreading. Recently, microwave envelope solitons have been observed in thin yttrium iron garnet (YIG) films for magnetostatic surface wave and forward volume wave configurations. In this work, we report the first observation of microwave envelope of magnetostatic backward volume waves (MSBVW) for an in‐plane magnetized YIG film with waves propagating parallel to the magnetization direction. Both soliton profiles and the nonlinear peak power response were observed. The experiments were conducted using a microstrip magnetostatic wave delay line structure. A single crystal YIG film of 7.2 &mgr;m thickness, 2 mm×15 mm in size, and with unpinned surface spins was magnetized in‐plane by a static external field of 1343 Oe along the long 15 mm edge. The 10 GHz ferromagnetic resonance linewidth of the film was 0.6 Oe. Square microwave pulses with pulse widths from 2 to 200 ns and a carrier frequency of 5.78 GHz were launched parallel to the field through a microstrip antenna. The output signal was received by a second microstrip antenna placed 4 mm downstream and analyzed in the time domain with a microwave transition analyzer. Envelope soliton behavior evident from the time resolved waveforms was observed for various input‐power/pulse‐width combinations.At relatively low power levels, one sees a broad output signal with a peak power increasing linearly with the input power. As the input power is increased above some threshold, a sharp soliton pulse emerges and the peak power increases more rapidly with input power than in the low power regime. The threshold varies with pulse width, as expected for solitons. A further increase of the input power produces multiple soliton profiles and a corresponding drop in the peak power. These results clearly demonstrate the existence of MSBVW solitons in YIG films. Dr. J. D. Adam of Westinghouse is acknowledged for providing the YIG films. This work was supported in part by the National Science Foundation, Grant No. DMR‐8921761 and by the U. S. Army Research Office, Grant No. DAAL03‐91‐G‐0327.

ISSN:0021-8979    

DOI:10.1063/1.354745

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The frequency dependence of the ferromagnetic resonance (FMR) linewidth and effective linewidth has been measured in Mn doped single crystal barium hexaferrite (BaFe12−xMnxO19) withx=0.1. Mn doped samples were used to minimize conductivity losses. Measurements were made onc‐plane thin disks magnetized to saturation along the disk axis andcdirection. A shorted waveguide technique was used to measure the FMR profiles in the range of 55–90 GHz. The FMR field position increased linearly at 0.35 kOe/GHz, with a zero field extrapolation of 34.7 GHz as expected for uniform mode FMR in barium ferrite. The linewidth &Dgr;H increased linearly with frequency at 0.29 Oe/GHz with a zero frequency extrapolation of 18 Oe. A high‐Q cavity method was used to measure the high field effective linewidth, &Dgr;HeffFFat 10, 20, 35, and 60 GHz. The effective linewidth increased linearly with frequency at 0.4 Oe/GHz, with a zero frequency extrapolation of 4 Oe. There were no dependencies of &Dgr;H or &Dgr;HeffFFon sample thickness. These results indicate that (1) eddy current contributions to &Dgr;H and &Dgr;HeffFFin these Mn doped barium ferrite materials are absent, (2) &Dgr;HeffFFis significantly lower than &Dgr;H and appears to be a good measure of the intrinsic losses, and (3) both linewidths increase linearly with frequency at about the same rate.These intrinsic linewidths in barium ferrite are still significantly greater than linewidths in yttrium iron garnet. Research sponsored in part by the United States Office of Naval Research, Contract No. N00014‐90‐J‐4078. The single crystal samples were kindly provided by M. A. Wittenauer, Purdue University.

ISSN:0021-8979    

DOI:10.1063/1.354747

出版商:AIP    

年代:1993

数据来源: AIP